Question:
how much current is drawn by the primary coil of a transformer of step down 220v to 22v to operate a device with an impedance of 220
Answer:
If the efficiency of the transformer is 100% -this is an assumption necessary to start from- the power delivered in the secondary must be equal to the power required in the primary coil.
So that, power in sec. coil = Wsec= (Vsec^2)/Zsec = (22^2)/220 = 2.2 W;
Where Vsec=22V Zsec=220Ohms Wsec = 2.2 W
In the primary coil Current = Iprim = Wsec/Vprim; Iprim = 2.2/220 = 0.01 A
Current is 10 mA
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